1. Field of Invention
This invention relates to electrical stimulation of cells in animals and other living forms, particularly to electrical stimulation of heart cells, including heart muscles associated with heart muscle contraction and purkinje and similar fibers, and more precisely, it relates to the art of causing an efficient contraction sequence of the heart muscle in order to maximize the volume of blood pumped per unit of energy spent by the heart. It also relates to the art of electrical stimulation of neurons as in brain and peripheral neurons. Brain neurons are stimulated both for clinical objectives, as in Parkinson's disease control, and in animal research as well, in which case neurons are stimulated to observe the consequences of the stimulation.
2. Discussion of Prior Art
The heart is divided into four chambers: left and right atria, at the upper part of the heart, and left and right ventricles, at the lower part of the heart. Right and left are conventionally assigned to be from the point of view of the person—which is the opposite left-right from the point of view of the observer looking at the person from the front. The atria are more holding chambers then actually pumping devices, evolved to quickly fill up the ventricles, below them, and consequently their walls are thinner when compared with the lower part, the ventricles. The right heart is responsible for the pulmonary circulation, receiving venous (non- or little-oxygenated) blood from the full body at the right atrium, passing it down to the right ventricle below it, from where the blood is pumped to the lungs. This corresponds to a short path, to the lungs and back. Back from the lungs, the blood enters the left atrium, which holds some oxygenated blood volume then releases it down to the left ventricle below it, from where the blood is then pumped to the whole body. The left heart pumps blood to the whole body, which involves more work when compared with the shorter path from the right heart to lungs and back, so the left atrium has thicker, stronger walls. These considerations on the wall thickness are of importance on our invention, because our invention deals with the optimization of the pumping mechanism of the heart, which is heavily dependent on the propagation delays of the electrical pulses that causes the pumping mechanism, as explained below.
The electrical nature of muscle contraction was first observed in the waning years of the 1700s by Luigi Galvani, who noticed that a frog's leg contracted when subjected to an electric current. Today it is known that all our muscles, from a blinking eye to a walking leg, work on the same principles observed by Galvani—including out heart. The heart contracts as response to an electric pulse, which is injected on it at the required frequency, which varies according to the person's activity and state of excitation. It is crucial here to keep in mind that this electric pulse does not propagate as the ordinary power in copper wires, which occurs very fast, virtually instantaneously, but propagates rather as a displacement of heavy ions inside and outside of the muscle cells, subjected to much scattering and other obstacles. In fact, the time elapsed between the initial contraction of the atrium, or upper heart chamber, and the ventricle, or lower heart chamber, is of the order of 120 to 200 ms—a rather long time for electronics events (long enough for an electric pulse on a power line to go completely around the earth. This slow propagation of the electrical pulse in the heart muscle is important for the working of our invention, so the reader is requested to keep this in mind.
Several malfunctions are possible to occur that hinder the proper functioning of the heart. Some are of a mechanical nature, a subject not bearing on our invention, while some are of an electrical nature, which is the focus of our invention, as described later on: our invention is an inventive method and means to cause a better propagation of the electric pulse that causes the heart to beat.
Given that a proper understanding of the mechanism of heart beating and of the propagation of the electrical pulse that determines it is crucial to the understanding of our invention, we proceed to a brief explanation of the mechanism of the heart beating. This is also necessary because our invention is based on two separated and insulated fields of knowledge: medicine & physiology and electrical engineering, which are separated well understood by two groups of persons, but hardly by the same individual.
There are a wealth of books on the subject, as Thaler (2003), where the reader with a non-medical background can get more detailed information. In short, most muscles capable of contracting are made of such cells that under normal conditions they have an excess of negative ions inside their cellular walls, which causes an excess of positive ions just outside their cellular walls, attracted there by ordinary electrostatic attraction. When in this condition, its normal condition, the cell is said to be polarized. If the cell loses its inner negativity, the language of electrophysiology describes this as a depolarization event. We here warn the reader that this is a poor choice of name, because the cell is still polarized when the electrophysiologists mention a depolarization event, but it becomes polarized on the opposite direction (positive inside it). By a sequence of well-know mechanism this acquisition of positive charges (depolarization as said in the trade, misnomer as it is) causes the cell to contract, that is, to decrease its length. This is the mechanism behind the blinking of our eyes, behind our walking—and also behind the heart contraction. It being an electric phenomenon, this event can be controlled by the injection of the appropriate electrical pulse in the heart muscle. This will be described in the sequel, and our invention bears on a twist on the man-made mechanism (heart pacemaker) designed to cause a heart pumping contraction sequence. Our invention improves on the propagation of the artificial electric pulse that causes a heart contraction (and pumping).
As a last preparation information we want to clarify that the heart pumping mechanism is a modification of a class of pumps called peristaltic pump, which causes the motion of the fluid, or pumping, with a progressive forward squeezing of the container, which forces the fluid forward. The reader is requested to keep this fact in mind as he reads the explanation of our invention, that the hearts functions with a progressive squeezing of its chambers, akin to the milking of a caw, during which process the milker progressively squeezes the caw's tit between its pointing finger and the thumb, then press the middle finger, squeezing the store liquid further down from the tit, then the annular than the little finger, at which point all the can be squeezed is out, the hand is opened to allow more milk to enter the tit and the process is repeated.
In short, most of the heart cells are part of the miocardium, which is a variety of a large group of other cells which are capable of contracting when subjected to the mechanism just described of depolarization. The pumping sequence consists of blood entering the heart at the top of the atrium (which is also the upper chamber), then a sequential downward pumping squeeze of the atrium which squeezes the blood into the lower ventricle. Then there is a problem because the exit of the ventricles is at its upper part, next to the entrance port from the atrium, so, if the squeezing continued downward there would be no place for the blood to go (no exit port at the bottom of the ventricle!). This problem is solved with the interruption of the downward propagating electric pulse at the intersection of these two chambers and a re-emission of another pulse through fast channels known as His fibers, left and right bundles and finally the Purkinjie fibers which release the electrical pulse at the base of the ventricle, which then begin squeezing from bottom to top, squeezing the blood upwards towards the exit port (the pulmonary vein at the right and the aorta at the left).
So, the heart's electrical system starts with an electrical pulse at the top of the right atrium, from a small group of cells known as the sino-atrial node (SA node or SAN), from where it propagates fast to the left atrium by special fibers that propagate the electric pulse better than the miocardio muscle does, which causes a downward contraction of the atrium, the right atrium first, then the left atrium a few milliseconds later. The electric pulse is then captured at the base of the atrium, preventing it from continuing down, it is then used by special cells called the atrial-ventricular node 550avn (AV node or AVN) to start a new pulse which is send through special conduits (special wires, so to say), known as the His bundle, then the right and left bundle branch, then the Purkinjie fibers, which then release the electrical pulse regenerated at the atrio-ventricular node 550avn at the lower part of the ventricle, causing now the ventricle to start contracting upwards, as needed to pump the blood to the upper exit port of the ventricles. This completes the heart cycle.
Electrical malfunctions of the heart may be more obvious faults as insufficient energy in the electrical pulse that causes the pumping or some more subtle ones as errors in the propagation of the electrical pulse. The original artificial heart pacemakers simply injected an electric pulse near the sino-atrial node SAN at the top of the right atrium, and later versions injected two or even three separate pulses in two or three different parts of the hearts. None of them, though, even attempted to control the path of the injected current once it is injected artificially—which is the object of our invention. In other words, our invention improves on the electrical propagation features of the electric pulse created by the artificial heart pacemakers, and in doing so it improves the squeezing sequence of the heart, which in turn improves the pumping efficiency. It is to be remembered that, because the heart is a variation of a peristaltic pump, the pumping sequence is of fundamental importance for an efficient pumping.
Originally heart pacemakers were simply an exposed wire tip, the wire connected to a battery and electronics circuitry to create pulses of appropriate frequency, shape and amplitude.
The original implant was made with an open chest surgery, but this was quickly supplanted by a less invasive and much less traumatic technique, with which an incision was made on some vein at the chest (usually the subclavian vein, on the upper chest), where a wire was inserted, which had some sort of screwing or anchoring ending at its distal extremity, then this wire was fed in until its distal extremity reached the upper right heart chamber, from the inside (the right atrium), where the wire tip was screwed on the inner part of the heart, near the natural starting point of the electrical pulse that causes the heart to beat, know as the sino-atrial node (SA node or SAN).
The proximal end of the wire was then connected to a battery and electronics box which was implanted in the chest, in some convenient location. From the wire tip anchored at the distal end, a current emanated, which then propagated through the heart muscle, causing the muscle to contract as the current proceeded along it, hopefully similarly to the naturally occurring electric pulse. It is crucial here to remember that this muscle contraction occurs because of the electric charge carried by it, and consequently, it is the electric current propagation time and pathway that determines the heart contraction sequence—because the muscle cells contract as a consequence of the electric charge near it. The sequence of muscle contraction is crucial for an efficient heart functioning, because the heart must start squeezing from its furthest end, away from the discharge exit area, most away from the exit port, continuously squeezing its wall towards the exit port. The heart does not contracts as a person squeezes a tennis ball for exercise, but rather, the heart squeezes sequentially pushing the blood forward, towards the exit port. An example of a similar contraction sequence, for similar objectives, is the milking of a caw, a process which requires that the milker starts squeezing the upper part of the tit, then continue squeezing lower and lower, while keeping the upper part squeezed to prevent the milk to move back, until the end of the tit is squeezed, at which point the milk previously lodged in the tit is moved out and the process starts again. The heart does not squeeze all the blood out of it, as much as the caw milking, cannot squeeze all the milk out of the tit. Most people get astonished when they learn that the heart pumps not much more than 50% of the blood in it—a rather low efficiency!
Over the more than 50 years of heart pacemaking, many types of electrode tips have been developed. Some of the electrode tips possessed some degree of symmetry, some not. Whether or not the tip electrode had or not symmetry, this quality was transferred to the current injected into the heart muscle. The heart, on the other hand, is asymmetric, particularly from the point of view of the point where the stimulating electrode is anchored in the heart, which often is near the sino-atrial node, or at the top of the right atrium. It follows that the current that is injected by current art heart pacemakers cannot follow well the contour of the heart muscle, causing a less than ideal contracting sequence. Other anchoring positions for the electrode are also used, and multiple electrodes as well, which may stimulate the atrium and the ventricle independently
In the former case, the tip symmetry had consequences on the current distribution in the heart muscle, because, at least initially, it caused a current symmetry. In the latter case, the lack of symmetry also had consequences on the current distribution, because it caused an initial asymmetric current injection, which could or could not be the ideal for the heart contraction sequence. In either case, the trajectory of current injection has not been controlled by prior art devices, which was a major problem as acknowledged by cardiologists working in the field of electrophysiology. This lack of control of the current distribution, as it propagated through the heart muscle, plagued all the earlier art of heart pacemakers, and still does in current art.
Throughout the years, many variations were introduced in the electrodes, as the shape of the wire tip, which served to anchor it in place, but these changes were largely for mechanical reasons, as to provide a more secure anchoring of the electrode on the heart muscle, or to minimize physical damage to the heart tissues, etc. Changes have also occurred on the method of introducing it in the heart, but most of these were changes to solve other problems, not to induce a good squeezing sequence of the heart muscle. Consequently, the uncontrolled propagation of the electric current from the tip has been a constant. Attempts to improve the electric pulse propagation include the use of multiple wire tips, which injected current not only at different locations but also at different times, or with relative time delay between the stimulating places. Examples of such multiple site stimulation are atrial and ventricular stimulators, two tips, one at the atrium, another at the ventricle, which deliver a pulse with a time lag between them, corresponding to the time lag between atrial contraction and ventricular contraction. But these multiple stimulating tips are not designed to control the electric field—which determines the path of the injected electric current, which follows the electric field lines because these are the force lines.
Such multiple electrodes, usually, though not consistently, worked better than a single electrode. Yet, this lack of optimization of the heart muscle contraction has been a major problem known to the practitioners of the art. This uncontrolled propagation was shared by most, if not all models and their variations, in spite of the fact that the cardiologists were aware that uncontrolled electric pulse propagation caused inefficient heart pumping. Cardiologists knew that they had to address the problem of electric pulse propagation through the heart, but they have so far not succeeded in this goal. It has been a known problem in heart pacemakers, yet and amazingly, a problem which has defied solution for decades.
Moreover, even if multiple stimulating tips caused an improvement of the pumping squeezing sequence and efficiency, it had the detrimental effect of causing more muscle damage, as each anchored wire tip is a foreign body in the heart, also a foreign body which by necessity caused an injure to it, an injury which resulted in a scar tissue, which in turn has different electrical conductivity when compared with the normal heart, creating a problem spot for the very objective of controlled electric pulse propagation. Another problem was that, since often times the first attempt to anchor the tip in the endocardio is unsuccessful, either for mechanical or for electrical reasons, for every unsuccessful attempt the surgeon has to retract the tip then screw it again somewhere else, and occasionally even more than two attempts, each tip were usually responsible for multiple scars in the inner heart, which in turn posed limits to any dream of using a multiplicity of stimulating tips.
It seems that all prior art attempted to solve the problem of electric pulse propagation inside the heart muscle tissues with the use of multiple electrodes, while nobody succeeded to control the current propagation, in direction and magnitude, using one single electrode. Nor have prior art made full use of multiple electrodes to more completely shape the electric field within the heart muscle—which is the same as the electrical current path, because the electric field lines are the same as the force lines, or the lines along which the injected charges move.
Prior art simply used an arbitrarily shaped stimulating electrode, which than created a non-controlled electric field in the surrounding space, which in turn guided the injected charges (or electric current). Our invention offers a method and a means to adjust the electric field, independently from the stimulating electrodes, to the best shape depending on the particular case, as needed.